The invention relates generally to electrical connectors and, more particularly, to far end crosstalk reduction in electrical connectors.
Some electrical systems, such as network switches or a computer server with switching capability, include large backplanes with several switch cards and line cards plugged into the backplane. When cards are plugged into both sides of a circuit board, the circuit board is called a midplane. Generally, the line cards bring data from external sources into the system. The switch cards contain circuitry that may switch data from one line card to another. Traces in the backplane interconnect the line cards and the appropriate switch cards.
Some signal loss is inherent in a trace through printed circuit board material. As the number of card connections increases, more traces are required in the backplane. The increased number of traces and the length of the traces in the backplane introduce more and more signal loss in the backplane, particularly at higher signal speeds. Signal loss problems may be addressed by keeping traces in the backplane as short as possible. Connectors are sometimes oriented orthogonally on both sides of a midplane. With orthogonal connectors, the number and lengths of traces in the midplane may be reduced, thereby reducing trace losses in the midplane. Moreover, when connectors connect directly through the midplane, there are no traces.
Typically, some amount of crosstalk is present in electrical connectors, including orthogonal connectors. When multiple signals are carried through a connector, such as a connector carrying multiple pairs of differential signals, crosstalk coupling may occur in adjacent signal lines. If the coupled energy is sufficient, bit errors may be generated in an adjacent signal line. Crosstalk propagates in both directions in the adjacent lines. Near end crosstalk refers to crosstalk that propagates in the direction opposite to that of the aggressor signal, or the signal generating the crosstalk. Far end crosstalk refers to crosstalk that propagates in the same direction as the aggressor signal. Far end crosstalk is additive. That is, far end noise builds upon itself, or is cumulative. In some applications, because of its additive quality, far end crosstalk tends to be the most troublesome.
While non-orthogonal connectors have been developed that include some amount of noise cancellation, noise cancellation, or more specifically, far end crosstalk cancellation in orthogonal connector systems remains a challenge.